The focus of this application is on the hormonal and paracrine regulation of spermatogenesis in humans and rodents. Project I (Barry Zirkin and Jonathan Jarow) addresses the biological mechanisms that explain why only some men who receive hormonal contraception become azoospermic. Naturally occurring ethnic differences in the response to testosterone (T)-based contraception will be studied to address this biological issue. We will compare intratesticular concentrations of bioactive androgen in Asian and Caucasian men before and after they receive hormone-based contraceptive doses of T, and will determine the quantitative relationship between hCG [human chorionic gonadotropin]-induced intratesticular bioactive androgens and spermatogenesis. These studies should provide important new information needed to develop an effective hormone-based male contraceptive, as well as provide substantial new insight into the physiological mechanisms through which T regulates spermatogenesis in men. The biological effects of androgens on spermatogenesis are mediated via the androgen receptor (AR) in Sertoli cells. The primary objective of Project II (Terry Brown) is to elucidate the molecular mechanisms that drive expression of the AR gene in Sertoli cells and to identify the specific transcription factors and their cis-acting regulatory elements that control the pubertal maturation dependent and adult stage-specific transcription of the AR gene. Project III (William Wright) focuses on paracrine regulation of spermatogenesis by examining the in vivo function of Sertoli cell growth factors, GDNF, FGF-2 and IGF-1, which have been implicated as involved in the control of stem spermatogonial replication and differentiation. Its central hypothesis is that differentiated germ cells, via feedback effects, regulate the expression by Sertoli cells of growth factors that, in turn, regulate the differentiation and replication of stem spermatogonia. Finally, we propose a Pilot Project (Paul Miller) that is based on our understanding that germ cell DNA is subject to damage and may be an important factor in male infertility. A rapid, simple analytical method to assess the level of oxidative DNA damage in germ cells will be developed using beacon aptamers, oligonucleotides that have the ability to bind ligands in a highly specific manner. These biosensors will be designed to measure oxidized nucleosides, 8-oxodeoxyadenosine and 8-oxodeoxyguanosine, in the DNA of sperm from infertile men.